Practical and Highly Enantioselective Synthesis of β-Alkynyl-β-amino Esters through Ag-Catalyzed Asymmetric Mannich Reactions of Silylketene Acetals and Alkynyl Imines

A readily available iso-leucine-based phosphine ligand is used to promote Ag-catalyzed Mannich reactions between silylketene acetals and various alkynyl imines. Reactions can be effected in the presence of 5 mol % catalyst, without the need for rigorous exclusion of air, and with commercially available solvents (without purification) to afford the desired β-alkynyl-β-amino esters in 84−94% ee and 61−91% isolated yield.